Previous devices and transducers for measuring micromovements or linear displacements to high degrees of accuracy are known in the field which rely on interferometry, capacitance or quantum tunnelling.
X-ray interferometers currently provide the highest sensitivity down to the picometre scale. However these interferometers are very large, unwieldy and expensive. Accordingly, they are impractical for use in many situations and applications since they require a complex and rigorous mechanical setup and arrangement of components.
Capacitive micromovement measuring devices work by using the change in capacitance caused by a micromovement altering the separation distance between the capacitor's plates. This change in capacitance is detected and used to calculate the amount of displacement of the plates. Generally it is found that the greater the sensitivity of a capacitive micromovement measuring device the narrower the measurement range over which they are able to measure.
USSR Author's Certificate No. 947 626 discloses a micromovement measurement device that calculates micromovements down to the sub micron scale over a relatively large measurement range, of the order 1 millimeter. This device functions based on the detection of a loss of physical and electrical contact between a pair of contacts when a micromovement occurs and the use of a spring to force the contacts back together restoring physical and electrical contact. In this device elastic micro-strain and micro-deformation of the contacts occur due to the spring forcing the contacts together and electro-erosions can take place at the contacts, so affecting their geometry and leading to a reduction of the measuring accuracy and stability of the measurements.
Quantum tunnelling devices such as a scanning tunnelling microscope (STM) suffer from a narrow measurement range of the order of nanometres. This can be broadened by utilizing piezoelectric material to move the STM probe tip. However, for the micromovement to be measured in this manner, it would require piezoelectric material which can be accurately controlled to an extremely high precision. A further problem with STM's are their bulk, complexity and cost which effectively prohibits their use in certain situations and applications.
The closest prior art to the present invention is WO-A-02/42800. This discloses a micromovement measuring device which works by detecting an interruption in a field electronic emission current caused by a test object undergoing a micromovement. A fixing electromagnet and a pulling electromagnet are utilized to bring the tips sufficiently proximal so that the field electronic emission current is restored after the micromovement.
The present invention, in its broadest form, is characterised by those features set out in the characterising portions of the independent claims.
Devices according to the present invention provide highly accurate and sensitive micromovement measurements, both linear and angular. Embodiments of the present invention are able to detect displacements of a few Angstroms, while also providing a relatively large dynamic and substantially linear measuring range, for example up to 1 mm.
Devices manufactured in accordance with the present invention are expected to find applications in a very large number of fields including, though not limited to: pressure sensors including atmospheric pressure sensors, infrasound sensors, soliton wave sensors, shear wave sensors, pressure wave sensors, seismic activity sensors, burglar alarms, thermal sensors, humidity sensors, gravity sensors, accelerometers, force sensors, electric field sensors, magnetic field sensors, and gravity wave sensors.
When movement detection is combined with a micro-actuating device, the number of potential applications increases still further. Currently available actuators working at the nanometre movement range often slip, and it is necessary to monitor their movement with a separate device. Potential applications for a combined actuator and measurement system include the following:                Life Sciences, Medicine and Biology: Scanning microscopy, Patch clamping, Gene manipulation, Cell penetration, Micro dispensing.        Semiconductors and Microelectronics: Nano-metrology, wafer and mask positioning/alignment, critical dimension measurement, micro lithography, inspection systems, vibration cancellation.        Optics, photonics, fibre-Optics metrology and measuring Technology: Fibre optic alignment and switching, image stabilisation, adaptive optics, scanning microscopy, auto-focus systems, interferometry, adaptive and active optics, laser tuning, mirror positioning.        Precision Mechanics and Mechanical Engineering: Fast tool servos, out-of-roundness finishes (boring, drilling, turning), vibration cancellation, smart structures/structural deformation, wear correction, needle-valve actuation, micro-pumps, knife edge control in extrusion tools, micro-engraving systems.        